1. Field of the Invention
The present invention relates to a reversible thermosensitive recording material, and more particularly to a reversible thermosensitive recording material capable of writing (or displaying) information in a reversible thermosensitive recording layer of the recording material and erasing the same information therefrom utilizing the property that the transparency or color tone of the recording layer is reversibly changeable depending upon the temperature thereof.
2. Discussion of the Background
The conventional reversible thermosensitive recording materials have the drawback that a reversible thermosensitive recording layer is easily damaged by the application of heat and pressure thereto when the writing and erasing operations are repeatedly carried out using a thermal head.
To eliminate the above-mentioned drawback, it is proposed that a thermosetting resin (in Japanese Laid-Open Patent Application 7-132681); and an electron irradiation curing resin or ultraviolet curing resin (in Japanese Laid-Open Patent Application 7-172072) are employed for the formation of a reversible thermosensitive recording layer.
However, when the thermosetting resin is used for the formation of the recording layer, the setting of the recording layer proceeds with time, thereby changing the reversibility of the recording layer.
In addition, when the resin for use in the recording layer is subjected to electron irradiation curing, the curing reaction involves deoxidation. As a result, the color change takes place in the recording layer, and a support under the recording layer is readily corroded when a metal-deposited support is employed.
Furthermore, in the case where the recording layer is formed by curing the ultraviolet curing resin, the image contrast becomes poor after the repeated writing and erasing operations. The reason for such insufficient image contrast is that particles of an organic low-molecular weight material become large, so that refraction happens at the interfaces between the large particles of the organic low-molecular weight material and a binder agent in the recording layer, and therefore, the recording layer tends to be opaque as a whole.
In Japanese Laid-Open Patent Application 5-193258, there is disclosed a reversible thermosensitive recording material comprising a support, and an anchor layer and a reversible thermosensitive recording layer which are successively overlaid on the support. According to this application, spacer particles in the form of sphere, branch, and needle are dispersed in the recording layer or the anchor layer in order to prevent the decrease of the milky whiteness degree of the recording layer and improve the durability of the recording layer. Although the durability of the recording layer is considerably improved in fact, the image contrast is still insufficient for practical use.